In percussive rock drilling it is known to use what is called torque control, which aims at keeping the rotating pressure of the rotation motor of the rock drilling machine constant by adjusting the feed device of the rock drilling machine. When the rotation torque increases, the feed is decreased so as to re-obtain desired rotation torque. If, despite the decrease in the feed, the rotation torque does not get lower, the result may be drilling with underfeeding. In addition, the result may be that the drill bit gets stuck. As generally known, one problem with drilling with underfeeding is that the contact between the drill bit and the rock is reduced, which leads to a reduction in the drilling power. Further, underfeeding may result in tensile stress in the drilling equipment, which loads the joints between the drilling rods.
The invention relates to a method for controlling percussive rock drilling, the method comprising: controlling a percussion device in a rock drilling machine that gives impact pulses to a tool connected to the rock drilling machine during the drilling; controlling a rotating device in the rock drilling machine, the tool being rotated around its longitudinal axis during the drilling; controlling a feed device feeding the rock drilling machine during the drilling towards the rock to be drilled and correspondingly backwards; determining, during the drilling, at least rotation resistance, and registering a first moment of time when the rotation resistance exceeds a predetermined reference limit for the rotation resistance; and decreasing the feed to control the rotation resistance towards the predetermined reference limit for the rotation resistance.
The invention further relates to a software product for controlling percussive rock drilling, the execution of the software product in a control unit controlling the rock drilling being arranged to provide at least the following actions: to control, in a rock drilling machine, a percussion device for giving impact pulses to a tool connected to the rock drilling machine during the drilling, a rotating device for rotating the tool around its longitudinal axis during the drilling, and a feed device for feeding the rock drilling machine during the drilling towards the rock to be drilled and correspondingly backwards; and further, to determine, during the drilling, at least rotation resistance, and to register a first moment of time when the rotation resistance exceeds a predetermined reference limit for the rotation resistance; and to decrease the feed to control the rotation resistance towards the predetermined reference limit for the rotation resistance.
Still further, the invention relates to a rock drilling rig comprising: a carrier; at least one feed beam; at least one rock drilling machine movably arranged on the feed beam; a feed device for feeding the rock drilling machine towards the rock to be drilled and correspondingly backwards; the rock drilling machine comprising a percussion device for generating impact pulses for a tool connected to the rock drilling machine, and a rotating device for rotating the tool around its longitudinal axis; at least one control unit for controlling the functions of at least the feed device, percussion device and rotating device in accordance with a control strategy in the control unit; and means for determining at least rotation resistance; and the control unit being arranged to register a first moment of time when the rotation resistance exceeds a predetermined reference limit for the rotation resistance, and to decrease the feed for controlling the rotation resistance towards the predetermined reference limit for the rotation resistance.